The discovery of highly stable organic peracid molecules is critical to the commercialization of detergent formulations containing peracid bleaches. Such peracids have recently been discovered which are highly crystalline and have relatively high melting points. Also, it is highly important for highly stable bleaches to be prepared in a manner which eliminates, or at least minimizes contamination from metals. Metals or metal ions are particularly deleterious to peracids because they catalyze the decomposition of the peroxygen group.
Consequently, the detergent industry requires peracids which are highly stable, have high melting points and are conveniently manufactured in high volume. Because of their high melting points both the peracids and their precursors are typically purified by precipitation or crystallization techniques. Metal ions typically present in the crystallization media become trapped in the peracid crystals and become impurities which reduce the stability of the peracid. The amount of metal ion contamination is directly related to stability of the peracid.
A recent patent, U.S. Pat. No. 4,634,551 to Burns et al describes novel, relatively stable and high melting crystalline amide peracids. Generally, the precursors to these amide peracids, that is, the amido acids, were reported to have been prepared by the reaction of the appropriate acid chloride with the appropriate amine followed by precipitation of the resulting amido acid.
The peroxyacids found in U.S. Pat. No. 4,634,551 are represented by the formula ##STR1## where in R.sup.1 is selected from the groups consisting of alkyl, aryl or alkaryl radicals containing from about 1 to about 14 carbon atoms, R.sup.2 is an alkylene group containing from 2 to 14 carbon atoms and R.sup.3 is H or an alkyl, aryl or alkaryl group containing from 1 to about 10 carbon atoms, the total number of carbon atoms being from about 10 to about 20.
It has been found that the most efficient way to prepare the amide peracids is to first prepare the diester of a dibasic acid and then react the diester with an amine to provide a mono amido ester which can then be converted to the amide peracid. Such a process provides high yields of high quality product. This process also avoids acid chlorides which are relatively expensive and increases the burden of waste disposal. However, most processes for the production of the mono amido ester from the reaction of a diester with an amine produces a mixture of compounds and most prominently an undesired amount of the very stable diamide which has no economically attractive utility.
The reaction of an alkyl amine with, for example, the diester of adipic acid is well known as in U.S. Pat. No. 3,417,114 to Kueski. It is noted therein that esters of mono-, di, tri, or tetracarboxlyic acids may be employed wherein the resulting amide may contain one or more ester groups, depending on the extent to which the ester groups are converted to amide groups. However, no indication is given as to how to provide a selective reaction to produce a mono amido ester of a dibasic acid.
The production of amides by reaction in a column is described in U.S. Pat. No. 3,324,179 to Scholz et al. This patent discloses the reaction of four carbon fatty acids with alkylamines wherein the amine reactant is in excess or at least in stoichiometric amounts. Reflux ratios in the range of 2:1 to 30:1 are disclosed.
The production of methyl formamide by the reaction of ammonia and methyl formate in a reaction column is disclosed in U.S. Pat. No. 4,659,866 to Kaspar et al. It is reported that virtually quantitative conversion to the amide is provided in a continuous process. However, this process involves the conversion of a monoester to a monoamide.
Diamides are prepared in high purity according to U.S. Pat. No. 3,296,303 to Nemec et al by the reaction of a secondary amine with a diacid or diester wherein the diester is derived from selected ethylene or propylene glycols. The amidation step is conducted by employing the amine in a ratio with the ester or acid of at least 2:1. The process seeks to avoid the production of a mixture containing monoester amides.
Amides are also produced in the presence of water at relatively low temperatures by employing catalysts according to U.K. 1,108,395. There is reference to conducting such reactions in a column. Amides are prepared at temperatures of less than 30.degree. C. with catalysts, consisting of ion exchange resins, either strongly basic or strongly acid.
The reaction of esters with amines to provide amides is also disclosed in U.K. 631,367 to Meade which teaches the use of a basic catalyst consisting of an alkali metal alcoholoxide.
Although considerable work has been done in the art of preparing amides, the provision of a selective reaction of an amine with a dibasic acid to provide a high proportion of mono amido ester of such dibasic acid has not heretofore been discovered. In the production of large quantities of such material it is vital to reduce the amount of unwanted production of diamides to provide an environmentally sound, mass production process yet provide reasonably rapid reaction rates to provide the mono amido ester.
Attempts to provide the mono amido ester of dicarboxylic acids has resulted in a relatively low yield of the desired product. The above mentioned patent to Kuceski indicates recovery from a catalyzed reaction of about 40% by weight of the mono amido ester of adipic acid, based upon the weight of the original starting material.
It is therefor desirable to have a process for producing mono amido esters of dibasic acids which proceeds quickly and selectively so as to minimize the production of the diamide.